Field of the Invention
The present invention relates in general to the field of electronics, and more specifically to a system and method for three phase power quality measurement using asynchronous, isolated single phase circuits
Description of the Related Art
Utility companies and other companies provide electrical power to many customers. The particular loads that utilize the electrical power can affect the quality of the delivered power. Accordingly, many entities utilize power measuring systems to measure characteristics of the power delivered to one or more loads.
FIG. 1 depicts a power distribution system 100 that includes a power measurement system 102 that measures various characteristics of the three phase power delivered to the loads 104, 106, and 108. Loads 104, 106, and 108 can be any type of load including resistive, reactive, or resistive and reactive. The power distribution system 100 includes a phase A voltage VA, a phase B voltage VB, a phase C voltage VC, and a neutral conductor N. FIG. 2 depicts ideal waveforms 200 representing the phase A voltage VA, the phase B voltage VB, the phase C voltage VC. In at least one embodiment, the voltages VA, VB, and VC have a nominal fundamental line frequency of 60 Hz and a nominal root mean square (RMS) voltage of 110V in the United States of America and a nominal 50 Hz and a nominal RMS voltage of 220V in Europe.
Referring to FIGS. 1 and 2, in at least one embodiment, the A, B, and C phases and the neutral N are connected in a well-known wye configuration. In at least one embodiment, when the phases are connected in a delta configuration, the neutral N is omitted. Ideally the phase A voltage VA, the phase B voltage VB, and the phase C voltage VC have phases that are exactly 120° apart. However, the loads 104, 106, and 108 can cause the phase relationships to vary. Variation of the phase relationships can damage one or more of the loads 104, 106, and 108.
To determine the phase relationships, the power measurement system 102 includes a monolithic phase sequence and phase angle detector integrated circuit (IC) 110. The monolithic IC senses the voltages VA, VB, and VC on respective channels 112, 114, and 116 via voltage dividers 118, 120, and 122 and utilizes a single, high frequency clock signal CLK_HF. The high frequency clock signal CLK_HF provides a synchronous clock signal that allows the monolithic IC 110 to coordinate sampling of the voltages VA, VB, and VC, to determine the phase sequence and phase angle relationships between the voltages VA, VB, and VC. An exemplary frequency of the high frequency clock signal CLK_HF is 4 MHz. The monolithic IC provides the phase sequence and phase angle relationships in the respective signals PHASE_SEQ and PHASE_ANGLES for display, transmission, or storage in a memory for subsequent access.
However, implementation of a high frequency clock signal CLK_HF implies more sophisticated hardware in the monolithic IC 102 and increased power consumption than a slower determination of the phase sequence and phase angle relationships between the voltages VA, VB, and VC. Additionally, in at least one embodiment, because the voltage channels 112, 114, and 116 are not isolated in the monolithic IC 102, utilizing shunt resistor sensing of currents related to the voltages VA, VB, and VC is impractical.